substitute() with ampersand in replacement

Question

I’m doing something like this:

let l:new = substitute(l:old, l:word, l:repl, ‘’)

l:repl comes from an external source and often has an ampersand in it. Is there a way to prevent vim from interpreting the & as a sub-replace-special? The docs say that with nomagic, & is just &, but I can’t find a way to make nomagic apply to the replacement text.

I suppose one way would be to do an additional substitute() to replace & with \&, but that seems… stupid.

Example tests, using l:old = “Hello friends”, l:word = “friends”, and l:repl = Alice & Bob:

• echo substitute(l:old, l:word, l:repl, ‘’) → Hello Alice friends Bob
• echo substitute(l:old, ‘\M’.l:word, l:repl, ‘’) → Hello Alice friends Bob
• echo substitute(l:old, ‘\V’.l:word, l:repl, ‘’) → Hello Alice friends Bob
• echo substitute(l:old, ‘\V’.l:word, substitute(l:repl, ‘&’, ‘\\&’, ‘’), ‘’) → Hello Alice & Bob

So the last one works but is annoying and involves extra function calls.

I’ve also tried using the ex version, but with the same results.

Answer 1

:h 'magic' only applies to :h :s command. :h substitute() function always works as if :set magic (and this is for sure written on its help page).

Therefore one must escape his stuff before invoking substitute(). The preferred option is

:echo substitute(l:old, l:word, escape(l:repl, '&\'), 'g')